It is customary to clean the water in swimming pools and spas by withdrawing water from the lowest point in the pool or spa, filtering it, and then returning it to the pool or spa at a point just below the remaining water's surface. In the case of a swimming pool, the system usually includes a "skimmer" for drawing a portion of the circulating water from the upper surface of the body of water. That arrangement facilitates cleaning of the water, and is almost universally employed. In the case of the spa, the inlet is usually placed somewhat lower, and is made the inlet for air as well as water. The air and water are often combined in an aspirating venturi or in a Jacuzzi valve. That arrangement is used to admit a high velocity stream of water and air bubbles as well as being selected to facilitate cleaning of the water.
Thus it is that swimming pools and spas are plumbed and a circulating pump is provided to withdraw water from the low point in the body of pool or spa water and to return it at a higher point, usually near the surface of the body of water. The water circuit includes the outlet, a pump, a filter and the inlet, in series, and the pump usually precedes the filter.
Heating of the water, if that is to be done, is accomplished in a heater unit which is included in series in that circuit between the outlet and inlet. There may be an arrangement for bypassing the heater during intervals when the heater is not in operation, but when in operation the heater is connected in series with the cleaning circuit.
As a consequence of that arrangement, the water in pools and spas is heated by withdrawing cold water from the bottom and supplying heated water to the upper region of the pool. The warm water, being less dense, rises in the pool and the spa and cold water settles to the lower regions. That has some convenience for bathers use the water in the upper regions more than they do the lower water. However. it is found to have a very great disadvantage in that much energy is wasted when heating from the top downward as it requires replacement of the cold water by warm water.
It is one purpose of this invention to provide methods and means for overcoming that disadvantage in large measure.